Anybody know why in the reduce stage the value is null? Code below map stage:

var rec_data = JSON.parse(context.value);
        log.debug({title: log_title, details: 'rec_data' + JSON.stringify(rec_data)});

        context.write({
            key: rec_data.values.custrecord_aw_bt_transaction_type,
            value: rec_data
        });

Based on the logs, context.value has data, but when I get to the reduce stage, logs show: context.value:undefined